<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
     div{
         width: 300px;
         background-color: rgba(0,0,0,0.3);
         padding: 10px;
         position: relative;
     }
     input{
         width: 260px;
         border: 20px;
         padding: 10px 20px;
     }
     img{
         position: absolute;
         top: 14px;
         right: 30px;
     }
     p{
         color: red;
         margin: 0;
         font-size: 12px;
     }
    </style>
</head>
<body>
<div>
    <input type="text" placeholder="请输入用户名">
    <img src="http://doc.canglaoshi.org/tstore_v1/images/login/yhm.png" alt="">
    <p>用户名不能为空</p>
</div>
</body>
</html>